Filter assemblies have been employed in a variety of applications including hydraulic systems, fuel systems and engine lubrication systems. Such assemblies heretofore have used replaceable filter elements that can be installed on a filter head for filtering fluid flowing between inlet and outlet passages in the filter head. The filter element typically is contained within a housing such as a can that can be screwed onto or off of the filter head. In a so-called spin-on filter, the can is discarded along with the filter element. In other arrangements, only the filter element is replaced and the housing is reused.
During use the filter element may become clogged to the point that is causes a problem in the system, such as inadequate flow to components downstream of the filter, excessive pressure upstream of the filter element, and/or damage to the filter element allowing the accumulated contaminants to flow to components downstream of the filter element. Normally this is avoided by scheduled replacement of the filter element, but sometimes this is not done at the scheduled time or the filter element becomes clogged prior to the scheduled replacement because of particularly dirty conditions, for example. Consequently, provision heretofore has been made to allow fluid to bypass the filter element to allow for adequate, albeit unfiltered flow to components downstream of the filter element, to prevent damage to the filter element, and/or to prevent excessive pressure buildup upstream of the filter element. Fluid bypass is also desirable to avoid problems created during cold starts and flow surge conditions. Heretofore bypass valves were provided in the filter head for diverting flow from the inlet passage directly to the outlet passage, and thus bypassing the filter element, when the pressure differential across the filter element exceeded a prescribed amount.